In the article we will try to tell you in detail about what duplex communication is. This is the principle of connecting the receiver and transmitter, which implies the transmission of information simultaneously in both directions. For the first time, the concept of such a connection was implemented a century and a half ago in the transatlantic telegraph and a little later in teleprinters. Such an idea perfectly saved physical communication channels. Imagine how much a cable would cost to lay across the ocean floor. You can see for yourself - the savings are significant. In the case of a teletype, everything is much simpler. The idea was already known to everyone, but they came up with a slightly different way of displaying information (using printing devices).
Simplex systems
Simplex and duplex communication are, one might say, synonyms. But there are differences in the principle of transmitting and receiving information. In the case of duplex communication, several devices can simultaneously exchange information (receive and transmit it). But when organizing simplex communication, first one device broadcasts, then the second, the third, etc.e. In other words, there is some order.
Here are examples of simplex systems:
- Broadcasting.
- Microphones for sound recording.
- Baby monitors.
- Wireless and wired headphones.
- Various security cameras.
- Wireless control systems for any devices.
Simplex communication does not need to be able to transfer information in both directions.
The principle of operation of duplex devices
As for duplex communication devices, they have a slightly different design. They connect two points. An example is modern computer ports such as Ethernet. It is in them that such an exchange of information usually takes place. A similar principle is laid down in telephone communications - after all, you know very well that two people can talk and hear at the same time.
In digital technology, there is only the appearance of the effect of duplex radio communication (and wired too). If the receiving and transmitting channels actually worked simultaneously, the equipment would burn out in a matter of seconds. There is a certain time division, with its help, packets are formed and switched. And users who use communication tools cannot notice the "trick". There is a so-called incomplete duplex, which is actively used in walkie-talkies. In this case, the channel is broken by introducing certain code words that pronouncesubscribers.
How channels are divided by time
As the next example, we will consider the World Wide Web - the Internet. It is here that the separation of channels and the allocation of time intervals to various subscribers is important. These are lines with asymmetric speeds (there is both upload and download of data at the same time). The disparity of channels for different information streams made it possible to realize access to satellites. With such access, the request is made to the nearest network of the mobile operator, and the answer is already coming from the satellite from the depths of space.
Here are examples of devices using these technologies:
- Third generation of cellular communication (more familiar designation 3G).
- Several varieties of LTE.
- WiMAX (or 3G+).
- As well as the lesser known wireless DECT telephony.
Varieties of information transmission
A little over 50 years ago, impulse devices began to be widely introduced. The reason for its mass introduction is that solid-state electronics has appeared and has proven itself well. Discrete tube devices took up too much space (compared to more advanced semiconductor devices).
Initially there were two modes in which channels were compressed:
- Cyclic (synchronous) transmission type – subscribers connect to the line periodically. Moreover, the connection sequence is strictly specified. Firstyou need to design the frame structure, then implement the timing signals. As for the nature of the encoding, it doesn't matter.
- Asynchronous transmission type is widely used in digital systems. In this case, information is sent in pre-formed packets, the size of which is several hundred or even thousands of bits. Since there are addresses, it becomes possible to organize asynchronous interaction. This principle is used today even in cellular communications. You need to pay attention to the fact that in modern communication protocols the number of bytes is even. For this reason, there is no synchronization purely formally.
Signal frequency and shape
It should also be noted that each packet of information is supplemented by a header. The composition of the transmitted information is determined by which standard the protocol has. The channel is loaded with a certain period and frequency. Soviet duplex communication channels operated at a frequency of 8 kHz (the telephone signal is sampled at a rate of 64 kbps).
Note several methods of carrier frequency modulation:
- PWM (pulse width).
- Time-pulse.
- Pulse-amplitude.
Binary types of signals are encoded using square wave pulses. In this case, an infinitely wide spectrum is obtained, and the true signal can be cut using filters. The result of this is the smoothing of the fronts. Due to stretching, interpulse interference occurs. Interference appears in adjacent channels - this is due to the fact that the spectraintersect.
Steps of time separation
And now let's look at what stages of signal separation can be found in duplex intercoms. We can distinguish the following hierarchy:
- There are 32 channels on the first stage, two of them are reserved for service messages. The total speed of these channels is 2048 kbps.
- The remaining stages are formed by multiplexing four streams (bit by bit). It should be noted that all sections of the standards are formed in advance.
Frequency division
And finally, let's talk about frequency division. It was first put into practice by the signalman G. G. Ignatiev in 1880. The signal transmitter generates a certain set of analog type pulses (usually 12 of them). The signal width is standard - in the range of 300-3500 Hz. The block has the required number of generators operating in this range.
Frequency division can be called ideal for organizing symmetrical traffic channels. It is actively used in ADSL, IEEE 802.16, CDMA2000.
